1. Field of the Invention
The present invention relates to a fluid bearing apparatus and more particularly to a fluid bearing apparatus having an increased contacting area of a bearing and rotating elements and a compact size.
2. Description of the Related Art
Recently, with improvements in the fields of information and computer technology, there has arisen a need for rotary shafts with higher rotational speed and accuracy, but without unwanted movement or oscillation. Such rotary shafts are needed in driving motors for various machines, such as a polygon mirror driving gear of a laser printer, a spindle motor of a hard disk, a head driving motor of a video cassette recorder, and the like. A driving motor capable of stable rotating at high speed while preventing the movement or oscillation of the rotary shaft has been developed together with a fluid bearing apparatus which enables the rotary shaft of the driving motor to rotate at high speed with high accuracy.
The fluid bearing apparatus, as described above, generally has dynamic pressure generating flutes formed therein. There are two types of the dynamic pressure generating flutes. One type of the dynamic pressure generating flutes is a spiral shape and the other type is a herringbone shape. The spiral shaped dynamic pressure generating flutes are mainly applied to thrust bearings supporting thrust load and the herringbone shaped dynamic pressure generating flutes are mainly applied to radial bearings supporting a radial load.
In the case of a conical fluid bearing apparatus, one of the conventional fluid bearing apparatus, various structures have been proposed to provide sufficient rising forces in a short time for rotating elements, such as a bushing, a plate, and the like.
FIG. 1 is a cross-sectional view of a conventional driving apparatus of a polygon mirror, in which a conical bearing apparatus is applied to the driving apparatus to increase a contact area of a bushing and a shaft.
The conical bearing 70 includes a body 45 and an upper cone 45a and a lower cone 45b which are respectively formed at both ends of the body 45, while extending from one end of a fixing shaft 40. The body 45 connects the upper cone 45a to the lower cone 45b and has a predetermined diameter. Furthermore, the upper and lower cones 45a and 45b have tapered sectional shapes and extend outwardly from the body 45. The dynamic pressure generating flutes 45a', 45b' are respectively formed on the tapered surface of the upper and lower cones 45a and 45b. When the rotating elements rotate, the dynamic pressure is generated in the bearing resulting in shifting up the upper and lower bushing 30 and 32. In FIG. 1, reference numerals 10, 50, and 60 respectively indicate a polygon mirror, a plate having a rotor mounted thereon, and a lower bearing bracket.
In the bearing apparatus as constructed above, however, the upper cone 45a which is formed at one end of the body 45 is made to extend in the lengthwise direction of the fixing shaft 40 so that the cross-section area is gradually reduced from the one end of the body 45 to the top of the cone 45a. Thus, the height of the upper bushing 30 is increased as much as the length of the upper cone 45a. Therefore, there is a problem in that a total size of the motor is increased.